A solid polymer electrolyte fuel cell is expected to be a future energy-generation apparatus because the solid polymer electrolyte fuel cell has high energy conversion efficiency, is clean, and produces very little noise. In particular, the solid polymer electrolyte fuel cell has recently been used not only as a generator for automobiles and homes, but has also been installed into small electrical instruments such as cellular phones, laptop computers, and digital cameras because of its high energy density to possibly operate for a longer period of time than a conventional secondary battery, and has been attracting attention. However, cost reduction is required for a solid polymer electrolyte fuel cell used as a generator for automobiles and homes, and a catalyst usage is desirably reduced as a way for cost reduction. Practical application of a solid polymer electrolyte fuel cell as a generator for small electrical instruments requires a compact total system and improved power generation efficiency.
Conventionally, an attempt has been made at forming a catalyst into fine particles and supporting the catalyst on carbon particles or the like for three-dimensional dispersion, to thereby increase a surface area and improve catalyst utilization.
Meanwhile, another attempt has been made at forming a catalyst layer into a very small thickness of about several μm, to thereby facilitate substance transport. Further, a catalyst layer was gathered in a vicinity of an electrolyte membrane, to thereby increase an effective surface area of the catalyst.
In particular, in a case where a fuel cell is installed into small electrical instruments, the fuel cell itself needs to be small, and air is often supplied to an air electrode from air holes through natural diffusion (air breathing system) without use of a pump or a blower.
In this case, substance transport at the air electrode often becomes a reaction rate-limiting factor, and thickness reduction of a catalyst layer seems to be effective means. An example of a method of forming a thin catalyst layer involves deposition of Pt or the like on a surface of an electrolyte membrane through sputtering (see S. Y. Cha and W. M. Lee, “J. Electrochem. Soc.”, 146, 4055 (1999).